A circuit board (sometimes referred to as a printed circuit board or a printed wiring board) is the basic building block for interconnecting electronic devices in a system. Electronic devices, usually integrated circuit (IC) devices, are mounted onto the circuit boards using a number of mounting mechanisms, such as by use of connectors or by directly mounting the devices onto a surface of the circuit board. A circuit board also includes the wiring required to interconnect the devices electrically.
The number and density of signal lines in a circuit board are continuously increasing due to the increased density of circuits that can be formed on each IC chip. The number of input/output (I/O) pins that exist on each IC chip can be quite large, which means that a large number of signal wires are used to carry signals from one IC chip to another component in the system. To increase the density of signal wires that can be provided in the circuit board, a circuit board is usually formed of multiple layers. Some layers contain signal wires for transmitting signals, while other layers contain power reference planes, which are connected to ground or to a power supply voltage, e.g., a three-volt voltage, a five-volt voltage, or some other power supply voltage. In other arrangements of circuit boards, power reference planes are not used.
With large numbers of IC chips and signal wires (I/O circuits) in a circuit board, switching noise can be a problem during system operation, especially at high frequencies. To mitigate switching noise, surface mount technology (SMT) decoupling capacitors can be used. These capacitors can be mounted to either the primary or secondary (top or bottom) surface of the circuit board, and connected to reference planes through vias. At high frequencies, a capacitor provides a low impedance bypass path for switching noise between the power supply voltage plane and the ground plane.
In other implementations, SMT decoupling capacitors can be embedded between layers of a circuit board. Conventionally, SMT capacitors usually have a parallelepiped geometric shape provided in a manner in which the capacitor is taller than it is wide. To reduce spacing between layers of the circuit board, the capacitors when embedded in a circuit board are mounted on their sides (in a horizontal configuration rather than a vertical configuration).
However, an issue presented by placing an SMT capacitor on its side is that the conductive electrodes of the capacitor provided on the top and bottom of the capacitor may short circuit power reference layers that sandwich the SMT capacitor. An example of such a conventional arrangement is depicted in FIG. 1, which shows an SMT capacitor 10 placed on its side (note that the length L of the capacitor 10 is greater than its width W). The SMT capacitor 10 has a first conductive electrode 12 and a second conductive electrode 14. The SMT capacitor 10 is provided between power reference layers 16 and 18 of a circuit board. The electrode 12 is electrically contacted to the power reference layer 18, and the electrode 14 is electrically contacted to the power reference layer 16. To prevent undesired shorting of the electrode 12 to the power reference layer 16, an insulating layer 20 is provided between the electrode 12 and the power reference layer 16, and to prevent undesired shorting of the electrode 14 to the power reference layer 18, another insulating layer 22 is provided between the electrode 14 and the power reference layer 18. Shorting of the capacitor electrode 12 to the power reference layer 16 or shorting of the capacitor electrode 14 to the power reference layer 18 will cause the power reference layers 16 and 18 to be shorted to each other through the capacitor electrode.
An issue associated with the arrangement of FIG. 1 is that having to provide the insulating layers 20 and 22 adds complexity (and therefore cost) to the manufacturing process of a circuit board. If the insulating layers 20 and 22 are not properly positioned, undesired shorting can still occur between capacitor electrodes 12, 14 and power reference layers 16, 18.